In recent years, for color display devices used for image display such as in computers and television sets, a plasma display device using a plasma display panel (hereinafter, abbreviated as “PDP” or “panel”) receives attention as a large-size, thin, and lightweight color display device.
An AC surface-discharge-type PDP, which is a representative AC type, has a front panel formed with a glass substrate where scan electrodes and sustain electrodes are arranged for surface discharge; and a back panel made of a glass substrate formed with data electrodes being arranged. The front and back panels, arranged in parallel, are facing each other so that both scan and sustain electrodes, and data electrodes form a matrix, and also their gaps form discharge spaces. Its outer edge is sealed with a sealant such as glass frit. Further, discharge cells partitioned by barrier ribs are provided between the substrates, and phosphor layers are formed in the cell spaces between the barrier ribs. A PDP with such a makeup displays color images by exciting phosphors in red (R), green (G), and blue (B), with ultraviolet light generated by gas discharge for light emission.
Such an AC surface-discharge-type PDP is provided with a dielectric layer covering the electrodes on the front panel, and also with a protective film made of magnesium oxide (MgO) for protecting the dielectric layer. A method of modifying the surface of a protective film, requiring a high electron emission performance and anti-sputtering property, is disclosed for example in, Japanese Patent Unexamined Publication No. H08-236028, No. 2000-57939, and No. 20007-6989.
In such an AC surface-discharge-type PDP, magnesium oxide (MgO) has the following problems as a protective film. That is, for magnesium oxide (MgO), the electronegativity of magnesium is low, and thus its crystal has a strong ionicity, prone to have positive electrification. Usually, magnesium oxide (MgO) has an interface with a large number of asperities and crystal defects, and positive charge of Mg ion is exposed all over the defects. Therefore, H2O, CO2, or a hydrocarbon gas (mostly, a resolvent from organic binders) generated in various processes of PDP manufacturing is adsorbed around the defects, causing discharge to be unstable and the discharge voltage to rise. In addition, the H2O, CO2, or hydrocarbon gas adsorbed to magnesium oxide (MgO) are emitted into the panel during discharge after the panel is produced, to be adsorbed to the phosphor surface. This causes oxidative and reducing reactions to non-crystallize the surface of the phosphor particles, resulting in a low brightness.
The present invention aims at providing a PDP with a stable discharge characteristic and low brightness degradation, by implementing a protective film made of magnesium oxide (MgO) with a low gas adsorption.